1. Field of Technology
The present disclosure relates to articles including master alloy, and to certain methods of making and using those articles. More particularly, the present disclosure relates to formed articles including master alloy used for making alloying additions to a metal melt, and to certain methods of making and using such formed articles.
2. Description of the Background of the Technology
During production of stainless steel, titanium alloys, and other alloys, quantities of raw feed materials, often including scrap, are heated at high temperature to produce a melt having the desired elemental chemistry. It is often the case that quantities of one or more master alloys are added to the raw feed materials or to the melt to suitably adjust the elemental chemistry of the melt prior to solidifying the melt into an ingot, a billet, a powder, or some other form. As is known in the art, a master alloy is an alloy rich in one or more desired addition elements and is included in a metal melt to raise the percentage of the desired constituent in the melt. ASM Metals Handbook, Desk Edition (ASM Intern. 1998), p. 38.
Because the elemental composition of the master alloy is known, it theoretically is simple to determine what amount of a master alloy must be added to achieve the desired elemental chemistry in the melt. However, one must also consider whether all of the added quantity of the master alloy will be fully and homogenously incorporated into the melt. For example, if the actual amount of the master alloy addition that melts and becomes homogenously incorporated into the melt is less than the amount added, the elemental chemistry of the melt may not match the desired chemistry. Thus, an effort has been made to develop forms of master alloys that will easily melt and readily become homogenously incorporated into a metal melt.
One example of a specific area presenting some challenge is the introduction of certain alloying additives into a titanium melt. For example, it is difficult to alloy titanium with oxygen. Titanium sponge or cobble typically is used as the titanium-rich raw feed material when preparing titanium alloy melts. A conventional method of increasing the oxygen content of a titanium alloy melt involves compacting titanium sponge with powdered titanium dioxide (TiO2) master alloy. As the titanium dioxide master alloy dissolves and becomes incorporated into the melt, it increases the oxygen content of the molten material, and subsequently also increases the oxygen content of the solid material formed from the melt. The process of compacting the sponge and titanium dioxide powder has several drawbacks. For example, it is costly to weigh out and compact the materials. Also, preparing the compacted sponge and titanium dioxide powder requires a significant amount of time prior to the melting and solidifying/casting process.
A known alternative method for adding oxygen to a titanium melt is simply to mix a quantity of a loose powdered titanium dioxide master alloy with the titanium sponge and/or cobble raw feed materials in the melting vessel prior to heating the materials. In this method, relatively small amounts of the powdered titanium dioxide coat the surfaces of the sponge and/or cobble. If more of the powdered titanium dioxide is added, it will fail to stick to the starting materials and will segregate from those materials. This “free” titanium dioxide powder is prone to be carried away by air movement. Also, large portions of loose titanium dioxide powder that collect in the melting vessel may not be homogenously incorporated into the melt. Accordingly, a possible result of using this conventional titanium dioxide addition technique to adjust the chemistry of a titanium alloy melt is an inconsistent and unpredictable loss of titanium dioxide. The final result can be a titanium alloy product that does not have the expected elemental chemistry.
Given the above, titanium alloy producers typically use the alloying technique of adding loose powdered titanium dioxide when producing titanium alloys having small oxygen additions. Nevertheless, even in such cases the final level of oxygen achieved is somewhat unpredictable. When higher oxygen levels are desired than can be readily achieved by the addition of loose titanium dioxide powder, the titanium sponge/titanium dioxide powder compaction technique is often used, with the aforementioned lead time and cost disadvantages.
Given the drawbacks of conventional techniques of adding alloying oxygen to titanium melts, it would be advantageous to provide an improved alloying technique. More generally, it would be advantageous to provide an improved general technique for making various alloying additions to a wide variety of metal melts.